The viscosity of oils of lubricating viscosity is generally dependent upon temperature. As the temperature of the oil is increased, the viscosity usually decreases, and as the temperature is reduced, the viscosity usually increases.
The function of a viscosity improver is to reduce the extent of the decrease in viscosity as the temperature is raised or to reduce the extent of the increase in viscosity as the temperature is lowered, or both. Thus, a viscosity improver ameliorates the change of viscosity of an oil containing it with changes in temperature. The fluidity characteristics of the oil are improved.
Viscosity improvers are usually polymeric materials and are often referred to as viscosity index improvers.
Ester group containing polymers are well-known additives for improving the fluidity characteristic of lubricating oils. Polyacrylate, particularly polymethacrylate ester polymers, and esterified carboxy-containing intelpolymers are well-known and are widely used for this purpose.
Dispersants are also well-known in the lubricating art. Dispersants are employed in lubricants to keep impurities, particularly those formed during operation of mechanical devices such as internal combustion engines, automatic transmissions, etc. in suspension rather than allowing them to deposit as sludge or other deposits on the surfaces of lubricated parts.
Multifunctional additives that provide both viscosity improving properties and dispersant properties are likewise known in the art. Such products are described in numerous publications including Dieter Klamann, "Lubricants and Related Products", Verlag Chemie Gmbh (1984), pp 185-193; C. V. Smalheer and R. K. Smith "Lubricant Additives", Lezius-Hiles Co. (1967); M. W. Ranney, "Lubricant Additives", Noyes Data Corp. (1973), pp 92-145, M. W. Ranney, "Lubricant Additives, Recent Developments", Noyes Data Corp. (1978), pp 139-164; and M. W. Ranney, "Synthetic Oils and Additives for Lubricants", Noyes Data Corp. (1980), pp 96-166. Each of these publications is hereby expressly incorporated herein by reference.
It is desirable that the viscosity improver or dispersant viscosity improver not adversely affect the low-temperature viscosity of the lubricant containing same. Frequently, while many viscosity improvers or dispersant viscosity improvers enhance the high temperature viscosity characteristics of lubricating oil, that is, they reduce the loss of viscosity with increasing temperature, low temperature properties of the treated lubricant become worse.
One of the major requirements for automatic transmission fluids has been improved low temperature performance as demonstrated by a maximum Brookfield viscosity of 20,000 centipoise at -40.degree. C. The viscosity modifier, which can comprise nearly 50 weight percent of the total additive system employed in an automatic transmission fluid can have a major impact on the low temperature performance. Such characteristics are also desirable in other applications such as in gear lubricants. The copolymers of this invention are also useful in many other lubricating oil compositions including, but not limited to engine oils, hydraulic oils, industrial oils, etc.
Various pour point depressants, additives which reduce the temperature at which oil will flow freely, have been developed and those to reach the commercial market have primarily been organic polymers, although some monomeric substances such as tetra (long chain alkyl) silicates, phenyl tristearyloxy-silane, and pentaerythritol tetrastearate have been shown to be effective. Presently available commercial pour point depressants are believed to be represented by the following types of polymeric materials: polymethacrylates, for example, copolymers of various chain length alkyl methacrylates (see, for example, U.S. Pat. No. 2,655,479); polyacrylamides (see, for example, U.S. Pat. No. 2,387,501); Friedel-Crafts condensation products of chlorinated paraffin wax with naphthalene (see, for example, U.S. Pat. Nos. 1,815,022 and 2,015,748); Friedel-Crafts condensation products of chlorinated paraffin wax with phenol (see, for example, U.S. Pat. No. 2,191,498); and vinyl carboxylate, such as dialkyl fumarate copolymers (see, for example, U.S. Pat. Nos. 2,666,746; 2,721,877 and 2,721,878).
Esters of maleic anhydride/alpha-olefin copolymers have been suggested as pour point depressants. For example, U.S. Pat. No. 2,977,334 describes the use of copolymers of maleic anhydride and ethylene which are esterified with low or high molecular weight alcohols and/or amidized with an amine. These resins are described as being useful as pour point modifiers, gelling agents, thickeners, viscosity improvers, etc., for mineral and synthetic oils including functional fluids and lubricating oils. U.S. Pat. No. 2,992,987 describes a class of lubricant additives useful as pour point depressants which are ethylene-maleic anhydride copolymers esterified to 80% or more, preferably 90-100%, with a mixture of straight-chain saturated hydrocarbon alcohols having from 8 to 24 carbon atoms. The unesterified carboxylic groups can be left unreacted or can be reacted with such materials as ethylene or propylene oxide alcohol esters, or lower-dialkyl-amino-lower-alkylene-amines. U.S. Pat. Nos. 3,329,658 and 3,449,250 describe copolymers of maleic anhydride and alpha-olefins such as ethylene, propylene, isobutylene or vinyl aromatic compounds such as styrene as being useful dispersancy and detergency additives for oils, as well as pour point depressants and viscosity index improvers. The copolymer is esterified to about 30 to about 95% with aliphatic alcohols or mixtures of alcohols having from 10 to 20 carbon atoms, and the remaining carboxyl groups are reacted with an amine of the following formula: ##STR1##
where R.sub.1 and R.sub.2 are selected from the group consisting of aliphatic hydrocarbon radicals having from 1 to 4 carbon atoms and the cyclohexyl radical, R.sub.3 is an aliphatic hydrocarbon radical having from 2 to 4 carbon atoms, and R.sub.4 is selected from the group consisting of hydrogen and aliphatic hydrocarbon radicals having from 1 to 4 carbon atoms.
U.S. Pat. Nos. 3,702,300 and 3,933,761 (Coleman) describe carboxy-containing interpolymers in which some of the carboxy radicals are esterified and the remaining carboxy radicals are neutralized by reaction with a polyamino compound having one primary or secondary amino group and at least one mono-functional amino group, and indicate that such interpolymers are useful as viscosity index improving and anti-sludge agents in lubricating compositions and fuels. The patentee indicates that it is critical that the mixed esters described in these patents include both relatively high molecular weight carboxylic ester groups having at least eight aliphatic carbon atoms in the ester radical and relatively low molecular weight carboxylic ester groups having no more than seven aliphatic carbon atoms in the ester radical.
U.S. Pat. No. 4,604,221 (Bryant et al)relates to interpolymers similar to those described in the aforementioned '300 and '761 patents, except the ester groups contain at least 8 carbon atoms in the ester radical.
U.S. Pat. No. 5,124,059 (Koch et al)describes esters of similar interpolymers characterized by the presence within its polymeric structure of the following groups which are derived from carboxy groups of said interpolymer:
(A) at least one carboxylic ester group having at least 8 aliphatic carbon atoms in the ester group; PA1 (B) at least one carboxylic ester group having an ester group of the formula ##STR2## PA1 wherein R is a hydrocarbyl group of about 1 to about 50 carbon atoms, R' is a hydrocarbyl group of about 1 to about 50 carbon atoms, y is a number in the range of zero to about 50 and z is a number in the range of zero to about 50 with the proviso that both y and z cannot be zero; and optionally PA1 (C) at least one carboxylic ester group having no more than 7 aliphatic carbon atoms in the ester group. PA1 (A) an esterified carboxy-containing interpolymer, said interpolymer being derived from at least two monomers, (i) one of said monomers being at least one vinyl aromatic monomer and (ii) the other of said monomers being at least one alpha, beta-unsaturated acylating agent, and having, before esterification, number average molecular weight (M.sub.n) determined by gel permeation chromatography ranging from about 8,000 to about 350,000, wherein from about 80 to about 99% of the carboxylic groups of said interpolymer are esterified, wherein from about 80 to about 100% of the ester groups contain from 8 to about 23 carbon atoms and from 0 to about 20% of the ester groups contain from 2 to 7 carbon atoms, with PA1 (B) a hydrocarbyl substituted carboxylic acid or functional derivative thereof wherein the hydrocarbyl group comprises from about 10 to about 400 carbon atoms, and PA1 (C) an amine having an average of more than 1 condensable N--H group, in any order or simultaneously, or with the preformed reaction product of (B) and (C) wherein said preformed reaction product has at least one condensable N--H group. PA1 Tacx, J. C. J. F et al, Polymer, Vol. 37, 4307-4310 (1996); PA1 Chow, C. D., J. Applied Poly. Sci., Vol. 20, 1619-1626 (1976); and PA1 Baruah, S. D. et al, ibid., Vol. 60, 649-658 (1996).
U.S. Pat. No. 3,956,149 issued to Coleman relates to a lubricant or fuel composition containing a nitrogen-containing ester of a carboxy-containing interpolymer.
U.S. Pat. No. 3,959,159 issued to Coleman relates to lubricating compositions containing a nitrogen-containing mixed ester of a carboxy-containing interpolymer.
U.S. Pat. No. 4,284,414 issued to Bryant relates to a crude oil composition containing mixed alkyl esters of a carboxy-containing interpolymer.
U.S. Pat. No. 4,180,637 issued to Evani et al. relates to a process for preparing a low molecular weight carboxy-containing copolymer.
U.S. Pat. No. 4,200,720 issued to Evani et al. relates to a process for preparing a low molecular weight carboxy-containing interpolymer.
U.S. Pat. No. 3,085,994 issued to Muskat relates to a carboxy-containing interpolymer.
U.S. Pat. No. 3,388,106 issued to Muskat relates to a process for making a carboxy-containing interpolymer.
U.S. Pat. No. 3,392,155 issued to Muskat relates to a polyoxy alkylene glycol ester of a carboxy-containing interpolymer.
U.S. Pat. No. 5,157,088 (Dishong et al) relates to nitrogen-containing esters of carboxy-containing interpolymers having relatively low inherent viscosity.
U.S. Pat. No. 4,088,589 relates to lubricating oils blended from petroleum distillates and, if desired, a bright stock containing waxy or wax-like components and modified by the presence of copolymeric ethylene-higher alpha-olefins viscosity index improving agents, having their low temperature performance improved when said copolymer contains a minor weight proportion of ethylene by the addition of from 0.15 to 1%, based on the total weight of said lubricating oil composition of a combination of pour point depressants comprising: (a) from about 0.05 to about 0.75 wt. % of an oil-soluble condensation product of a chlorinated wax of from 10 to 50 carbon atoms and a mono- or dinuclear aromatic compound; and (b) from 0.05 to 0.75 wt. % of an oil soluble polymer of C.sub.10-18 alkyl acrylate and/or an interpolymer of a vinyl alcohol ester of a C.sub.2 to C.sub.18 alkanoic acid and di-(C.sub.4 -C.sub.18 alkyl) fumarate.
The Society of Automotive Engineers (SAE) has issued a standard, J-300 (December 1995), which defines limits for classification of engine lubricating oils in rheological terms. This standard contains limits for various engine oil viscosity grades. Also included in the standard are discussions of low temperature and of high temperature test methods.
Dispersant-viscosity improvers are frequently prepared by functionalizing, i.e., adding polar groups, to a hydrocarbon polymer backbone.
Hayashi, et al, U.S. Pat. No. 4,670,173 relates to compositions suitable for use as dispersant-viscosity improvers made by reacting an acylating reaction product which is formed by reacting a hydrogenated block copolymer and an alpha-beta olefinically unsaturated reagent in the presence of free-radical initiators, then reacting the acylating product with a primary amine and optionally with a polyamine and a mono-functional acid.
Chung et al., U.S. Pat. No. 5,035,821 relates to viscosity index improver-dispersants comprised of the reaction products of an ethylene copolymer grafted with ethylenically unsaturated carboxylic acid moieties, a polyamine having two or more primary amino groups or polyol and a high functionality long chain hydrocarbyl substituted dicarboxylic acid or anhydride.
Van Zon et al., U.S. Pat. No. 5,049,294, relates to dispersant/VI improvers produced by reacting an a alpha-beta unsaturated carboxylic acid with a selectively hydrogenated star-shaped polymer then reacting the product so formed with a long chain alkane-substituted carboxylic acid and with a C.sub.1 to C.sub.18 amine containing 1 to 8 nitrogen atoms and/or with an alkane polyol having at least two hydroxy groups or with the preformed product thereof.
Bloch et al., U.S. Pat. No. 4,517,104, relates to oil soluble viscosity improving ethylene copolymers reacted or grafted with ethylenically unsaturated carboxylic acid moieties then with polyamines having two or more primary amine groups and a carboxylic acid component or the preformed reaction product thereof.
Gutierrez et al., U.S. Pat. No. 4,632,769, describes oil-soluble viscosity improving ethylene copolymers reacted or grafted with ethylenically unsaturated carboxylic acid moieties and reacted with polyamines having two or more primary amine groups and a C.sub.22 to C.sub.28 olefin carboxylic acid component.
Steckel, U.S. Pat. No. 5,160,648 describes dispersant materials prepared by reacting highly condensed polyamines with carboxylic reactants and phenolic reactants.
Covitch, U.S. Pat. No. 5,707,943 describes mixtures of esterified carboxy-containing interpolymers, wherein residual acidity of the esterified interpolymers may be neutralized by reaction with an amine, and additive concentrates and lubricating oil compositions containing same.
Harrison et al in U.S. Pat. Nos. 5,821,205; 5,849,676; 5,851,965; 5,853,434 and 5,872,083 describe a succinimide composition prepared by reacting a mixture of an alkenyl or alkylsuccinic acid derivative, an unsaturated acidic reagent copolymer, and a polyamine under reactive conditions. The alkenyl or alkyl substituent of the alkenyl or alkylsuccinic acid derivative has Mn of from 1000 to 5000. The unsaturated acidic reagent copolymer is a copolymer of an unsaturated acidic reagent and an alkylene group. The alkylene group can be an .alpha.-olefin having 8 to 42 carbon atoms, a polyalkylene having from 8 to 28 carbon atoms, ethylene, styrene, 1,3-butadiene, vinyl alkyl ether having at least 3 carbon atoms, or vinyl alkanoate having at least 4 carbon atoms. The polyamine has at least 3 nitrogen atoms and 4 to 20 carbon atoms. The mixture contains from 0.5 to 10 equivalents of the alkenyl or alkylsuccinic acid derivative per equivalent of unsaturated acidic reagent copolymer and from 0.4 to 1.0 moles of polyamine per equivalent of alkenyl or alkylsuccinic acid derivative plus unsaturated acidic reagent copolymer.
Harrison et al in U.S. Pat. No. 5,716,912; describe a succinimide composition prepared by reacting a mixture of an alkenyl or alkylsuccinic acid derivative, an unsaturated acidic reagent copolymer, and a polyamine under reactive conditions; then treating the reaction product with either a cyclic carbonate or a linear mono- or polycarbonate or boron compound under reactive conditions. The alkenyl or alkyl substituent of the alkenyl or alkylsuccinic acid derivative has a Mn of from 1800 to 3000. The unsaturated acidic reagent copolymer has a Mn of from 2000 to 4800, and is a copolymer of an unsaturated acidic reagent and an olefin having an average of from 14 to 30 carbon atoms. The polyamine has at least 3 nitrogen atoms and 4 to 20 carbon atoms. The mixture contains from 1.5 to 10 equivalents of the alkenyl or alkylsuccinic acid derivative per equivalent of unsaturated acidic reagent copolymer and from 0.4 to 1.0 moles of polyamine per equivalent of alkenyl or alkylsuccinic acid derivative plus unsaturated acidic reagent copolymer.
Barr et al, (U.S. Pat. No. 5,670,462) discloses a process which comprises reacting at an elevated temperature a copolymer of an olefin and a monomer having the structure ##STR3##
wherein X and X.sup.1 are the same or different provided that at least one of X and X.sup.1 is such that the copolymer can function as a carboxylic acylating agent and a succinimide prepared from an acyclic hydrocarbyl substituted succinic acylating agent and a polyamine.
Wilby et al., (U.S. Pat. No. 5,719,108) disclose dispersant viscosity improvers for lubricating oils which comprise the reaction product of a copolymer of octadecene-1 and maleic anhydride, said copolymer having a number average molecular weight from greater than 6300 to less than 12000 and a succinimide prepared from a polyamine and an acyclic succinic acylating agent of the formula ##STR4##
wherein X and X.sup.1 are the same or different provided that at least one of X and X.sup.1 is such that the copolymer can function as a carboxylic acylating agent and optionally a primary or secondary hydrocarbyl monoamine., and optionally a compound having at least two primary or secondary amino groups separated by at least 3 carbon atoms.